Group B Strep (GBS) Testing

GBS is a common bacterium (bug) which is carried in the vagina and rectum in 2–4 in 10 women (20–40%) in the UK. GBS is not a sexually transmitted disease and most women carrying GBS will have no symptoms. Carrying GBS is not harmful to you but it can affect your baby around the time of birth. GBS can occasionally cause serious infection in newborn babies, and, very rarely, during pregnancy and before labour.

Many babies come into contact with GBS during labour or around birth. The vast majority of these babies will not become ill. However, if you carry GBS, there is a small chance that your baby will develop GBS infection and become seriously ill, or even die. Around 1 in every 1750 newborn babies in the UK and Ireland is diagnosed with early-onset GBS infection. The infections that GBS most commonly causes in newborn babies are sepsis (infection of the blood), pneumonia (infection in the lungs) and meningitis (infection of the fluid and lining around the brain). Although GBS infection can make your baby very unwell, with prompt treatment most babies will recover fully. However, of the babies who develop early-onset GBS infection, 1 in 19 (5.2%) will die and, of the survivors, 1 in 14 (7.4%) will have a long-term disability. On average in the UK, every month: 43 babies develop early-onset GBS infection 38 babies make a full recovery 3 babies survive with long-term physical or mental disabilities 2 babies die from their early-onset GBS infection.

Infection is more likely to happen if: your baby is born preterm (before 37 completed weeks of pregnancy) – the earlier your baby is born, the greater the risk you have previously had a baby affected by GBS infection you have had a high temperature or other signs of infection during labour you have had any positive urine or swab test for GBS in this pregnancy your waters have broken more than 24 hours before your baby is born.

A urine infection caused by GBS should be treated with antibiotic tablets straight away and you should also be offered antibiotics through a drip during labour. You should be offered antibiotics through a drip during labour if you have had a GBS-positive swab or urine test from an NHS or other accredited laboratory (see the GBSS website for further information: www.gbss.org.uk/TestingforGBS). If you have previously had a baby who was diagnosed with GBS infection, you should be offered antibiotics through a drip when you are in labour. If your waters break after 37 weeks of your pregnancy and you are known to carry GBS, you will be offered induction of labour straight away. This is to reduce the time that your baby is exposed to GBS before birth. You should also be offered antibiotics through a drip. Even if you are not known to carry GBS, if you develop any signs of infection in labour, you will be offered antibiotics through a drip that will treat a wide range of infections including GBS. If your labour starts before 37 weeks of your pregnancy, your healthcare professional will recommend that you have antibiotics through a drip even if you are not known to carry GBS.

If a previous baby was affected with GBS infection then you should be offered antibiotics during labour in all following pregnancies, as there is an increased risk that a future baby may also be affected. If, however, GBS was found in a previous pregnancy and your baby was unaffected, then there is a 1 in 2 (50%) chance that you will be carrying it again in this pregnancy. To help you choose whether you would like to have antibiotics in labour, you can have a specific swab test (known as the enriched culture medium or ECM test) to see whether you are carrying GBS when you are 35–37 weeks pregnant. If the result shows that: you are still carrying GBS at this stage of pregnancy then the risk of your baby developing early-onset GBS infection is increased to around 1 in 400 and you will be offered antibiotics in labour you are not carrying GBS at this stage of pregnancy then the risk of your baby developing early-onset GBS infection is much lower (1 in 5000) and you may choose not to have antibiotics.

The test for GBS is a simple swab (cotton bud) taken from just inside the vagina and another swab from just inside the rectum. This can be done by our healthcare staff or taken yourself. Once taken the swabs are placed into enriched culture medium and analysed at our UK based laboratory for the presence of GBS. Results are normally available within 3-5 days.

If you have been offered antibiotics to prevent GBS infection in your baby, these should be started as soon as possible after your labour begins, or after your waters have broken. They will be given through a drip and continued at regular intervals (usually 4-hourly) until your baby is born. You should still be able to move around freely during labour and this should not stop you from having a water birth. If your waters break before labour, your healthcare professional will talk to you about when you will need antibiotics and about the best time for your baby to be born. This will depend on your individual circumstances and on how many weeks pregnant you are. The antibiotic that you will be offered to prevent GBS infection in your baby is usually penicillin. If you are allergic to penicillin then you will be offered a suitable alternative.

The UK National Screening Committee does not recommend testing all pregnant women for the presence of GBS using vaginal and rectal swabs. This is because: many women carry the GBS bacteria and, in the majority of cases, their babies are born safely and do not develop an infection screening all women late in pregnancy cannot accurately predict which babies will develop GBS infection no screening test is entirely accurate: a negative swab test does not guarantee that you do not carry GBS many babies who are severely affected by GBS infection are born preterm, before the suggested time for screening (35–37 weeks) giving antibiotics to all women who carry GBS would mean that a very large number of women would receive treatment they do not need.

There are multiple sources of information about GBS in pregnancy available. We would recommend the following: Royal College of Obstetricians and Gynaecologists (RCOG) information Group B Strep Support NICE Clinical Guideline CG149 A full list of useful organisations is listed on the RCOG website